Violet flowers are borne above the foliage in late spring, although we admire the dramatic, low fans of broad leaves as much as the blooms. Foliage is very flat and neat, and holds up well throughout the summer, long after flowers have faded. Roof Iris grows vigorously and easily, tolerates light shade, and quickly forms dense clumps. A welcome short Iris for lightly shaded areas; yes, it has historically been planted on thatched roofs. Appreciates sharp drainage.